This invention relates to an injection nozzle for diesel engines with a directional injection into a combustion air in the combustion space displaced with a swirl, which injection nozzle is constructed as a hole-type nozzle with several injection openings arranged at uniform distances and distributed along a circumferential arc of the nozzle.
In the case of diesel engines, it is known to inject the fuel into the combustion space in such a manner that, before and during the combustion, it is distributed as uniformly as possible on the total combustion air. In this case, the direct fuel injection according to the spray atomization process is dominant in which the fuel is injected from a multihole nozzle downward into the combustion air in the combustion space, in which case, when this air flows in, it was set into a rotating motion about the cylinder axis as a result of a special shaping of the intake duct. As the result of the rotation of the air, the desired distribution of the fuel takes place on the whole combustion space, thus also on air which does not directly encounter the atomization of the fuel during the injection through nozzle bores.
As the result of this circulating air flow in the combustion space, particularly in the case of combustion processes with a high swirl, the injector sprays will have a strong drift. If the individual drifting sprays overlap in this case, local areas with a fuel excess are formed which burn while lacking oxygen. The consequences of such an incomplete combustion are high emissions of soot.
So that the injection sprays will not drift in an overlapping manner as described, in the case of this form of injection, injection nozzles are used which have a limited number of injection bores whose bore distance is selected such that the individual injection sprays cannot overlap even when there is a strong drift.
An injection nozzle of this type is described in European Patent Document EP-PS 0 246 373 B1 and is described there as a structural component of an overall fuel injection system. In the case of this known injection nozzle, a total of three injection openings are constructed at uniform distances from one another laterally on the circumference of the nozzle body.
According to the position of a valve closing element constructed as a hollow cylinder, the three injection openings are opened or closed and the fuel quantity to be injected is proportioned accordingly. When the injection openings are completely open and the injection pressure is defined, the fuel quantity which can be maximally injected is determined by the overall cross-sectional surface of the three injection openings which have the same size. The above-described overlapping of the injection sprays which are defined by the injection openings and the drifting of these injection sprays as the result of the combustion air swirl are avoided, in this case, because of the angular distance of 120.degree. respectively.
Because of its constructional and functional characteristics explained so far, this known injection nozzle has the disadvantages that, as the result of the few opening surfaces of the injection openings of the same respective diameter, a relatively small overall openings surface and, as a result, relatively long injection durations will be obtained. In addition, the air utilization is low in the case of the combustion operation of this swirling process with the conventional three to five injection openings.
It is therefore an object of the invention to provide an injection nozzle of the initially mentioned type which permits shorter injection durations and/or an improved air utilization while it avoids the above-described disadvantages.
Based on an injection nozzle of the above-mentioned type, these objects are achieved by providing an injection nozzle wherein, between at least two adjacent first size injection openings another second smaller size injection opening is constructed, the mouths of all injection openings being situated on a common circumferential arc.
This alternating arrangement of large and small injection openings, where in each case between two large bores, which were previously constructed also in the case of conventional nozzles of this type, according to the invention, an additional injection opening is provided which has a smaller bore diameter, has the technical advantage that therefore, with a view to the whole injection nozzle, a much larger total cross-sectional surface of all injection openings is achieved on a nozzle than in the case of conventional injection nozzles without any even partial drifting into one another of the resulting injection sprays during the injection into the air swirl.
The thus enlarged total cross-sectional injection surface permits a significantly higher fuel flow than in the case of conventional injection nozzles so that, under conventional injection pressure conditions, the provided fuel quantity can be injected into the combustion space during a much shorter period of time than previously. This shorter injection duration provides the advantage of a shorter combustion duration, whereby the effective specific fuel consumption can be lowered.
Another significant advantage of the construction of the injection opening according to the invention is the correspondingly achieved uniform distribution of the fuel in the air, which leads to a more homogeneous mixing and a resulting much better air utilization in the cylinder. In this case, the combination of small and large injection openings has a particularly advantageous effect because, by means of a constant injection pressure, a finer atomization is basically achieved by means of small injection openings than by means of large openings.
In a further development of the invention, it is provided that the axes of the large and the small injection openings are in each case situated on different concentric cone envelopes whose cone angles differ. As a special advantage of this embodiment, an injection pattern is achieved which excludes within an even higher degree of reliability an overlapping drifting of the injection sprays and, at the same time, promotes turbulent flow conditions for a better swirl of the fuel in the combustion air in the combustion space.
The significantly improved air utilization resulting from the homogeneous mixing and the therefore achieved sequence of the combustion leads to a lower development of soot while the pollutant emissions are otherwise the same.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.